Sintered desulfurizer for off-furnace use

ABSTRACT

A desulfurization composition for off-furnace use consisting of crushed particles of sintered material comprising 100 parts by weight of calcium oxide and 3 to 50 parts by weight, in total, of at least one compound selected from the group consisting of up to 30 parts by weight of calcium fluoride, sodium fluoride, magnesium fluoride, barium fluoride, and sodium silicofluoride, and up to 40 parts by weight, in terms of sodium carbonate, of sodium carbonate, sodium hydroxide, and sodium oxide.

United States Patent [191 Ooi et al.

[ 1 Feb. 13, 1973 41 SINTERED DESULFURIZER FOR, OFF- FURNACE USE [75]Inventors: Hiroshi Ooi; Hakaru Nakato, both of Chiba, Japan [73]Assignee: Kawasaki Steel Corporation, Fukigiku, Kobe (:ity, Japan [22]Filed: Oct. 21, 1970 [21] A i. No.: 82,717

[30] Foreign Application Priority Data Oct. 24, 1969 Japan ..44/84 663Sept. 24, 1970 Japan ..44/83224 Sept. 24, 1970 Japan ..45/83223 [521' ris. C|....' ..75/58, 75/94 [51]- Int. Cl. ..C2lb 1/10, C21b 3/02 [58]Field of Search ..75/58, 59, 76, 94, 55

[56] I References Cited UNITED STATES PATENTS 3,537,842 11/1970- Holland..75/58 3,598,573 8/1971 Trostberg et al. ..75/5S 3,615,354 10/1971Ramachandran ..75/58 Primary Examiner-L. Dewayne Rutledge AssistantExaminerJ. E. Legru Attorney-George F. Dvorak, Stephen T. Skrydlak andMarden S. Gordon 1 ABSTRACT A desulfurization composition foroff-furnace use consisting of crushed particles of sintered materialcomprising 100 parts by weight of calcium oxide and 3 to 50 parts byweight, in total, of at least one compound selected from the groupconsisting of up to 30 parts by weight of'calcium fluoride, sodiumfluoride, magnesi um fluoride, barium fluoride, and sodiumsilicofluoride, and up to 40 parts by weight, in terms of sodiumcarbonate, of sodium carbonate, sodium hydroxide, and sodium oxide.

6 Claims, 1 Drawing Figure PATENTEU FEB 1 3191a 05 8 Emma. B 22 oo 2 0633 mtoa crumuo 2 0 Time (minute) Tim EmEoo Bram SINTERED DESULFURIZER FOROFF-FURNACE USE This invention relates to a sintered desulfurizer foroff-furnace use, and more particularly to a desulfurizer consisting ofcrushed particles of sintered material which is suitable for off-furnaceuse.

Recently, the use of converters has noticeably expanded in steel-makingindustries, and in order to ensure high efficiency of converters,increasingly high quality'of molten pig iron is required as the inputmaterial thereto. Since it is particularly troublesome to added in thepig iron in the course of transferring the molten pig iron from theblast-furnace to the converter, which molten pig iron is usually carriedby a ladle.

After adding the desulfurizer, the ladle is preferably vibrated, shaken,or stirred for thoroughly mixing the desulfurizer with the molten pigiron.

Conventional desulfurizers for such purposes consist of calcium carbide(caC because calcium carbide has a high desulfurizing ability. Forinstance, by using 4 to 6 Kg of calcium carbide per one ton of moltenpig iron, 0.05 percent of sulfur-content can be reduced to 0.01 percent,or 80 percent of desulfurization can be achieved by such addition ofcalcium carbide.

Calcium carbide has another advantage in that it is available in solidphase and never melts by itself in the ladle while being stirred.Accordingly, such solid phase desulfurizer does not cause any chemicalreaction either with the refractory bricks on the ladle wall, or withthe blast-furnace slag. With the desulfurizer consisting of calciumcarbide, sulfur once isolated from the molten pig iron seldomredissolves in the molten iron. Furthermore, the slag formed by thedesulfurization by calcium carbide is easy to remove from the ladle.

On the other hand, calcium carbide has a serious drawback in that it israther expensive, and that it quickly reacts with water and generatesacetylene gas which is very easily inflammable. Accordingly, extra careis necessary in handling calcium carbide.

With the increase in the production of steel, the amount pig iron to bedesulfurized by calcium carbide has greatly increased. Accordingly, theexpenditure for the calcium carbide desulfurizer amounts to aconsiderable value. Accordingly, extra care is required to ensure thesafety of personnel handling the desulfurizer.

ln order to mitigate such shortcomings of calcium carbide, theapplicants have carried out a series of studies and experiments, and hassucceeded in finding out an improved desulfurizer for off-furnace usewhich is made by crushing sintered material of calcium oxide basecomposition.

Quick lime or calcium oxide itself has been known as a desulfurizer,which is mixed with a suitable flux material. When a known desulfurizerconsisting of calcium oxide and a flux is added in a molten pig iron,the

sulfur-capturing ability of the solid desulfurizer is extremely small,and reasonable sulfur-capturing ability can be obtained only after thecalcium oxide is melted. In order to facilitate the melting of suchdesulfurizer including calcium oxide, a large amount solvent (e.g.,silica SiO alumina Al O calcium fluoride CaF has to be added. The use oflarge amount of such solvents tends to cool the molten pig iron.

- In contrast to the aforesaid solid desulfurizer, the moltendesulfurizer consisting of calcium oxide corrodes refractory bricks ofthe ladle. Accordingly, such combination of quick lime and flux materialis not suitable for off-furnace use, because it causes temperaturereduction of the molten pig iron.

lt has been also known to add about 10 percent of soda ash (Na CO and/orcaustic soda (NaOH) in quick lime. The desulfurizing ability of suchmixture,

however, is inferior to that of calcium carbide. In fact,

the desulfurizing ability of such mixture in the case of pig ironcontaining 0.05 percent of sulfur is 50 percent when the mixture isadded at a rate of 10 Kg of the mixture per ton of the pig iron, 60 to65 percent when 20 Kg/ton, and 70 to 75 percent when Kg/ton. Thus, toachieve the same desulfurizing effects, about six times in weight ofsuch mixture has to be addedin comparison with calcium carbide. Althoughquick lime itself is fairly inexpensive, if a large amount of it isused, e.g., 20 Kg/ton, the total cost of desulfurizer consisting of suchmixture becomes almost comparable with that of calcium carbide.Furthermore, the use of a large amount of desulfurizer results in anincrease of slag, which means more man-hours for slag removal after thedesulfurization. Thus, the overall efficiency of the desulfurizingprocess with such mixture is fairly poor.

Japanese Patent Publication No. 29,867/1968 discloses a desulfurizerconsisting of a composite slag made by melting a mixture of quick'lime,calcium fluoride (CaF soda ash (Na CO caustic soda (NaOH), and/orcalcium carbide (CaC The desulfurizer of this Japanese Patent issuitable for final desulfurization of molten steel, which is refined ina special furnace, but it is not suitable for off-furnace pretreatmentof starting molten pig iron for steel-making,

because it requires special equipment while using a.

considerably large amount of heat requiring a large expense.

Therefore, an object of the present invention is to obviate theaforesaid difficulties of conventional quick lime base desulfurizer,which consists of a mere mixture of quick lime and flux material oramolten slag of quick lime with suitable additives, by providing animproved quick lime base desulfurizer. The desulfurizer of the presentinvention retains all the advantages of solid desulfurizer, inclusive ofa desulfurizing ability which is comparable with that of calciumcarbide. The desulfurizer of the invention is featured in its low cost,so that it is particularly suitable for the production of a largequantity of low-sulfur steel.

The desulfurizer for off-furnace use, according to the presentinvention, consists of crushed particles of sintered material comprisingparts by weight of calcium oxide and 3 to 50 parts by weight, in total,of at least one compound selected from the group consisting of up to 30parts by weight of calcium fluoride, sodium fluoride, magnesiumfluoride, barium fluoride, and

sodium silicofluoride, and up to 40 parts by weight, in terms of sodiumcarbonate, of sodium carbonate, sodium hydroxide, and sodium oxide.

What is meant by in terms of sodium carbonate refers to the number ofsodium atoms in each of such compounds. For instance, 40 parts by weightof sodium carbonate is equivalent to 30 parts by weight of sodiumhydroxide, as given by the following formula.

1 molecular Weight of NaOH .:40X 40 (1 molecular weight of Na CO )/2106/2 For a better understanding of the present invention, reference ismade. to the accompanying drawing, in

which a single drawing is a graph illustrating the results ofexperiments on some sintered desulfurizers of the present invention.

The invention will now be described referring to examples.

Example 1:

Specimens of desulfurizer of the invention were prepared by adding 3 to30 parts by weight of calcium fluoride having a particle size smallerthan 0.3 mm, in 100 parts by weight of a main ingredient consisting ofcalcium oxide of a particle size smaller than 0.3 mm, sintering themixture thus prepared at I,200,C to 1,600C, and crushing the sinteredproducts to a particle size of 3 mm or less.

Tests were made on the desulfurizing speed by using the aforesaidspecimens which consisted of different amounts of calcium fluoride addedin calcium oxide and sintered at I,300C. Each of the specimens for thetests was in the form of a sintered cylinder of 25 mm diameter and 30 mmheight. The specimen cylinders of the desulfurizer were immersed in amolten pig iron at l,350C, which contained about 0.07 percent of sulfur.Each specimen cylinder was rotated in the molten pig iron at 200 RPM.FIG. 1 shows the variation of sulfur content in the molten pig iron astime elapses.

For comparisons sake, test results with a known calcium carbidedesulfurizer are also shown in FIG. 1, which calcium carbidedesurfurizer was also sintered and shaped in the same cylindrical formas that of the desulfurizer specimens of the present invention.

It is apparent from FIG. 1 that the addition of calcium oxide alone doesnot cause any material reduction in sulfur-content of the pig iron,while the desulfurizing effects increase with the addition of calciumfluoride in the calcium oxide and the desulfurizing ability of thespecimens of the invention containing more than I parts by weight ofcalcium fluoride is superior to that of conventional calcium carbide.The desulfurizing speed of the desulfurizer of the invention increaseswith the content of calcium fluoride of up to about parts by weight, butwhen the additional quantity of calcium fluoride further increases,e.g., to 35 parts by weight, the desulfurizing speed 7 decreases,. asshown in the figure. Thus, the desulfurizing speed of the desulfurizerof the invention saturates at a certain addition quantity of theaforesaid compound in calcium oxide, for instance at about 30 parts byweight of calcium fluoride per 100 parts of calcium oxide.

It was confirmed by tests that desulfurizers of the inin detail byvention containing one or more of sodium flurode,

magnesium fluoride, and barium fluoride also had a similar desulfurizingability to that of FIG. 1. The suitable addition quantity of suchcompounds to calcium oxide was found to be 3 to 30 parts per I00 partsby weight of calcium oxide.

It was also found that the calcium oxide to be used in actualdesulfurization at plant can be replaced with calcium carbonate (CaCO orcalcium hydroxide (Ca(OH) which are less expensive than calcium oxide.The sintering temperatures of I,200C to 1,600C also apply to calciumcarbonate and calcium hydroxide base desulfurizers, which are crushedinto a particle size of 4 mm of less. According to the presentinvention, it is also possible to add a small amount, e.g., a few partsby weight per 100 parts of calcium oxide, of a suitable binder, such assodium dihydrogen phosphate, calcium chloride, starch, and clay. Withthe addition of clay, the pellets of the desulfurizer is improved, sothat during the sintering process, the shape of the desulfurizer pelletscan be kept intact, and its workability is improved.

In preparing the desulfurizer of the invention, it is preferable to keepthe'particle size of the main ingredient calcium oxide and additivecompound, e.g.,

calcium fluoride, to less than 0.3 mm, so as to shorten the sinteringtime and to achieve a higher desulfurizing ability.

As pointed out in the foregoing, calcium oxide alone is not effective indesulfurization, and what is effective in desulfurization seem to bedispersed mixture of calcium compound and the added compound, e.g.,calcium fluoride, which mixture has a structure consisting of moleculesof the ingredient compounds well dispersed therein by the sinteringprocess. Such fact was confirmed by microscopic tests of thedesulfurizer after the desulfurizing process.

If the particle size of the ingredients in the desulfurizer is toolarge, the sintering time increases. More particularly, if the particlesize of the ingredients exceeds 0.3 mm, it is difficult to producedesulfurizer having a sufflcient desulfurizing ability by sintering at I,200C, for several hours.

Table I shows the desulfurizing ability of simple mixtures of calciumoxide and calcium fluoride. Similarly, Table 2 shows the desulfurizingability of the sintered desulfurizers of the invention. Table 2 alsoindicates the desulfurizers of non-sintered quick lime basedesulfurizers containing calcium fluoride and sodium fluoride. Thedesulfurizing ability, or the rate of desulfurization, of Tables I and 2were determined by adding the desulfurizers in about 60 tons of moltenpig iron carried by a ladle, and stirring the contents of the ladle by agate-type impeller. The desulfurizers of Table 2 were prepared by mixingcalcium oxide having a particle size of about 0.2 mm with calciumfluoride having a similar particle size, sintering the mixture at I,300Cfor 30 minutes, and then crushing the sintered products into a particlesize of about 2 mm.

Table I Simple mixtures consisting of parts by weight of CaO and 20parts by weight of CaF, Temper- Quantity ature Sulfur- Sulfur- Rate ofdesulof Treating content, content, of furizer molten time before afterdesulin pig pig (minute) treating treating furiza iron iron (96) ('11)tion g 8.3 I350 10 0.043 0.023 46.5 8.4 I320 I0 0.045 0.028 37.8

hour after the desulfurization with the desulfurizers o the invention.

fluoride ingredient is contained i desulfurizer and has a very limite Itwas confirmed that no substantial redissolution of sulfur was noticed bystanding the molten pig ir The slag removal after desulfurizationby thedesulfurizers of the present invention proved to because the slag floatson the surface of t solid state.

ortant feature of the invention that the Sulfur Sulfur Rate of contentcontent desulbefore after furizang, treating, tion, percent w mwmm u m eHnte M h atrio 2 uu md rwcm H mmo .wSe Th am d r m mW C m .ld mo o l Xnf 6 a0 .1 g e v 058 & r. O r.r.S. t 3C m e r s ma i 5 i h m e il l k .lmnl fld e m k u h D. P] m 03 O X .l n C 7. all m fi ae u 0 8 c u lm ,hrR 1 VJS u T. a wfl s ua m n. "III" .7 iad ma 0n L I" T e 0 X n m s" Inre g.l .l0t T 2. e v .mm.m h m H M 1:11 H o tmv lm o IIII 1 n a i I iwe m mh fl nm E "III" .1 .1." t t 03 W 52.1 s h m o 1:1: H e. nyc mc b Yh ebai B III: a" t .l m ep w a w 0 S m 11050001 0402 57 l h1 m c H w m me m m m w m inunmaafimmainacn \1 0. P u ,c I mk WC mSO .w u n O a t ed 1.ld.la It b n c Zn Tmkam T n V ee tt p I l. .JJ n l i aas N H "1 11.101nV.lS e .p r 0 0 $4l5 2 l .w m fiw m U a t.m a n ne.m l N H Iae0 Oae m.m3 h ihh e n u H tpnE tst ptmil FLU 68 w w x m w mes ateeeteuseaaeas t346 0-45648888887866 4 w %mwmm%%w%%mumnmw%m uwmm m 00000000000000000 00000000000000000 000 00 0 ml wuumwmm%w%mwmmwm%m mm% 1 000000000000000000000 "n" 00 000 00 00000000000 000 mm I i m m m wm m m m mmm mm m s 5;.

-CaFz desulfuri mg time, treati minute percent percent zers of theinvention, as compared with known non-sintered desulfurizers] Quantityof Temperdesulature of [urizer molten Treatn p t; t;

iron, iron kg./ton. C.)

[sintered CaO CaF2 (parts in 100 parts of CaO) Not sintered.

The addition quantity of the binder in each specimen is shown in percentby weight, based on the total weight of CaCOa, NaaCOz, and CaFz.

1 In those specimens which were sintered at 1,000C

1- or 1,l00C, calcium carbonate was almost completely decomposed intothe form of calcium oxide, but in the specimens which were sintered at900C, most of the calcium carbonate was not decomposed. Tables 4-1 and4-2 show the compositions of the specimens thus prepared, in which thecontent of calcium oxide is used as the base, regardless of whether itis in the form of calcium oxide or calcium carbonate. Tables 4-l and 4-It is apparent from Tables 1 and 2 that the simp mixture of theingredients do not have a high desu furizing ability, but the sintereddesulfurizer of the invention has a very desulfurizing ability.

It should be noted here that the desulfurizer of the invention retainsthe advantages of solid state desulfurizcrs. More particularly, fluxwhich contains a fluoride usually tends to corrode the refractory brickof the ladle wall, but with the present invention, the

2 also give the desulfurizing ability of the specimens, as determined bytest operations. For comparisons sake, desulfurizers of known type werealso tested, and the results are shown in the Tables.

l,100C with an increased addition quantity.

if the sintering temperature is below 800C, the desired desulfurizingeffects cannot be achieved by using an economical amount of thedesulfurizer.

The desulfurizing abilities, or the rates ofclesulfuriza- 5 It is animportant feature of the resent invention i bl 4-1 d 4-2 were d i d bddi that the sintermg temperature of the desulfurrzer can thedesulfurizers into a ladle carrying 60,tons of molten be not ceablyreduced by using calc1um oxide material pig iron, and stirring thecontents of the ladle by a gat together w1th the aforesa1d sod1umcompounds. In fact, type impeller with a rotary member having twovertical the slntermg temperature of the desulfunzer of Examl 10 ple lin the range of 1,200C to 1,600C can be It is apparent from the Tables4-1 and 4-2 that excelreduced to the range of 900C to l,100C of Examplelent desulfurizing effects can be achieved by the desul- 2. As comparedw1th the treatmg temperature of furizers of the invention. If thesintering temperature is 2,000C to 2,500C necessary for the manufactureof below 800C, most of the calcium carbonate does not conventionalcalcium carbide desulfurizers, the dissociate, and such residual calciumcarbonate conaforesaid sintering temperature range of 900C to tainsabout 40 wt.% of carbon dioxide which does not 1,lC of this Example ofthe present invention is very participate in the desulfurization, sothat it becomes low, so that the desulfurizers of the invention ensuresnecessary to increase the addition quantity of such considerable economywhile retaining the high desuldesulfurizer in the molten pig iron. lnExample 2, the 20 furizing ability and other advantages of solid phase'desulfurizers which were sintered at 900C provided desulfurizers, asdescribed hereinbefore referring to similar high desulfurizing effectsas those sintered at Example 1.

.. TABLE 4-1 Amount Contents of ingredients, in of desul- Temper- Sulfurcontentin pig parts by weight per 100 Sinternig furizerin ature iron(percent) Rate of parts by weight of C00 tempermolten of pig Treatingdesulfur- Specimen ature pig iron iron time, Before After ization numberNazCO; NazO CaFz C (kg.,/ton) C.) minute treating treating (percent)Remark 2'1 1,100 6.5 1,390 10.0 0.051 0.030 41 Reference. 2-2 1,1000. 1. 430 10. 0 0. 033 0. 015 01 1, 100 (i. 5 l, 370 0. U 0. 048 0. 01070 H U 000 10. 0 1,350 0. 0 0. 044 0. 011 7 201 111. 0 1,100 0.5 1,41010. 0 0.01:1 0. 001 75 1 110 110,001,100, M 1, 100 0. 5 1, 350 0. 0 0.015 0. 010 71 J00 10. U 1, 3-10 (1.0 0.013 0.010 70 1,100 6. 5 l, 42010.0 0. (H2 (l. 008 75 1,000 0. 5 1,1110 0. 0 0. 045 0. 011 70 1, 000 0.5 1, 350 0. 0 0. 050 0. 010 00 1,000 6. 5 1,350 6.0 0. 055 0.000 841Theinvention. 1,000 0. 5 1, 350 0. 0 0. 04's 0. 014 00 1,000 0. 5 1, 2300. 0 0. 002 0. 023 03 1,100 6.5 1,1-160 6.0 0. 045 0.030 33 Reference.

1, 100 0. 5 1, 350 0. 0 0. 052 0. 025 52 000 10. 0 1, 2140 0. 0 0. 0150. 017 02 1, 100 0. 5 1, 1150 0. 0 0. 03s 0. 010 74 000 10.5 1, 300 0. 00. 040 0. 012 10 1,100 6.5 1,350 6.0 0.055 0.008 85 Theinvention.

TABLE 4-2 i Amount of Sulfur content SilltOP desulfnin pig iron Rate ofing rizer in Temper- 'Ir-eat- (percent) desul- Spou- (mutants ofingredients, in parts by weight per 100 parts by temmolten ature int:fnriza- 1111011 weight of U110 pornpig of pig: time Before After tionnnm- ture iron iron (mintrcatt1'111t- (por- |10r Nan/() Nnzt) Nat)NazSiFa N111" (11F (1111 (k n/ton) (3.) utv) 1111: i111; cent) Remark r1,100 0.5 1,300 0. 0 0.015 0.000 05 i 000 10. 0 1,350 0. 0 0.040 0.000110 1,100 0.5 1,250 0.0 0.050 0.007 00 2-21. 11. 0 5. 0 000 10. 0 1, 5100. 0 0. 044 0. 00s 32 0. 5 1, 350 0. 0 0. 05 1 0. 020 51 1, 100 0. 5 1,510 0. 0 0. 053 0.000 30 1 000 10.0 1,350 0.0 0. 054 0. 007 37 1,100 0.51 300 0.0 0. 050 0.012 f i 000 10.0 11200 0.0 0.055 0.012 73 1 0.5 1,370 0.0 0.000 0. 034 00 i '000 10.0 1,200 0. 0 0. 055 0. 02; 5s 1,1000.5 1 030 0.0 0.005 0.020 55 2 1 000 10.0 11300 0.0 0.045 0.021 51'Il1ein 1,100 0.5 1, 200 0.0 0.042 0.000 01 vention.

i 000 10.0 1,370 0. 0 0. 045 0000 so 2-211 1.5 5.0 1,000 0.5 1,350 0.00.055 0.010 02 TABLE 4-2 -('onlinued Amount of Sulfur COI'ltQiltfiSinter desulfuin pig iron Rate of ing rizer in Temper- Treat- (percent)desul- Spee- Contents of ingredients, in parts by weight per 100 partsby temmolten ature ing turizaimen weight of :10 perapig of pig timeBefore After t'ion numture iron iron (mintreattreat- (perber NazCO; NazONaOH NazSiFo NaF CaF CaF: C.) (kg/ton) C.) ute) ing ing cent) Remark 6.51, '560 6. 0 0. 045 0. 008 82 6. 1, 360 6.0. 0. 040 0.005 88 6. 5 1, 3506. e 0. 047 0.007 85 6. 5 1, 340 6.0 0. 055 0'. 0m 83 6. 5 1, 240 10.00.050 0. 012 76 6. 5 1, 230 10.0 0. 060 0. 012 80 6. 5 1, 260 6. 0 0.051 0. 006 88 6. 1, 340 10. 0 O: 045 O. 007 84 6.5 1, 380 10.0 0. 0560.010 82 1, 410 10.0 0. 013 U. 015 54. 5 15 1, 4'20 10. 0 0. 012 0. 01166 15 1, 670 6. 0 0. 045 0. 031 31 15 1, 250 6.0 0. 050 O. 0'28 44Reference. 15 350 6. O 0. 055 (i. 024 56 15 1, 340 10. 0 0. 045 0.021!35. 5 l5 1, 380 10. 0 (I. 056 0.015 37. 5 15 1,1560 6. 0 (i. 040 0.01757. 5 15 l, 330 10. 0 0. 060 0. 0 i2 17. l)

1 Not sintered.

Example 3:

Desulfurizers of the invention consisting of calcium carbonate andsodium silicofluoride were prepared by thoroughly mixing ingredients asshown in Table 5, each having a particle size of about 0.2 mm,-sintering the mixture at 1,300C for 30 minutes, and crushing thesintered product into particles of about 2 mm particle I size.

Table 5 Unit: parts by weight Specimen No. CaCO Na siF 3-1 98.9 1.1 3-297.3 2.7 3-3 94.2 5.8 3-4 92.3 7.7 3-5 85.6 14.4 36 83.6 l6.4

The desulfurizing ability of the desulfurizers of the invention thusprepared was tested by the same manner as Example 2, and the results areshown in Table 6. For comparisons sake, known desulfurizers of similarcomposition were prepared and tested. Table 6 also includes theproperties of such known desulfurizers.

It is apparent from Table 6 that the sintered and crushed desulfurizerof the present invention has excellow sintering temperature is as low asthat of simple mixture of the ingredients. On the other hand, forsintering at a temperature higher than 1,600C, the desulfurizing abilityof the products is not improved but the cost of the sintering furnaceand the sintering operation increases in vain. The excessively highsintering temperature is, of course, undesirable from heat economy. Theparticle size of the crushed particles of the sintered material ispreferably smaller than 4 mm, in order to achieve the desirable quickdesulfurizing speed for ensuring high efficiency in the desulfurizingprocess. More particularly, the desulfurizer of the present invention isa kind of solid desulfurizer, and from the macroscopic viewpoint, theparticles of the desulfurizer are not melted in the molten pig iron butthe particles act to capture sulfur at the surface thereof from themolten pig iron. As the sulfur is captured, the active surface area ofthe individual desulfurizer particles becomes smaller to reducedesulfurizing ability, and the desulfurizing time increases.Accordingly, the particle size of the desulfurizer should preferably besmaller than 4 mm.

What is claimed is:

l. A granular desulfurizer composition for quickly desulfurizing pigiron in off-furnace treatment consisting of crushed particles ofmaterial sintered at a temlent desulfurizing ability. 5O perature of8001 ,600C whereby the sulfur content TABLE 6 Contents of NlzSlFu inSulfur content parts by Amount of Temper in pig iron Rate of weight perSintorinr, desulfurizer nture (percent) desulfur- 100 parts temperinmolten of pig Treating ization Specimen by weight ntnrv pig iron irontime Before After (pernnmber of (130 0.) (kg/ton) C.) (minute) treatingtreating cent) Remark 2 1, 300 6. 5 1, 330 10 0.053 0. 026 51 Reference.5 1,300 6. 5 1, 340 10 0. 058 0. 014 T6 11 1, 300 6. 5 1, 350 6 0. 0400.006 85 The invention. 15 1, 300 6. 5 1. 330 10 O. 049 0. 007 86 1, 3006. 5 1, 370 10 0. 036 0. 008 78 1, 300 6. 5 1,390 10 O. 035 0. 012 66 1115 1,350 6 0. 040 0. 022 Reference.

I Not sintered.

The preferable temperature range for the sintering the material of thepresent invention is 800C to 1,600C. if the sintering temperature isbelow 800C, the desired sintering effects cannot be obtained, and thedesulfurizing ability of the products made by such a is substantiallyreduced, comprising .100 parts by weight of calcium oxide and 3 to partsby weight, in total, of at least one compound selected from the groupconsisting of up to 30 parts by weight of calcium fluoride, sodiumfluoride, magnesium fluoride, barium desulfurized in an'off-furnacetreatment.

2. The granular desulfurizer composition according to claim 1,consisting of crushed particles of sintered material comprising 100parts'by weight of calcium oxide and 3 to 30 parts by weight of at leastone compound selected from the group consisting of calcium fluoride,sodiumfluoride, magnesium fluoride, barium I fluoride and sodiumsilicofluoride.

3. The granular desulfurizer composition according to Claim 1,consisting of crushed particles of sintered material comprising 100parts by weight of calcium oxide and 3 to 40 parts by weight, in termsof sodium carbonate, of at least one compound selected from the groupconsisting of sodium carbonate, sodium hydroxide, and sodium oxide.

4. The granular desulfurizer composition according to Claim 1,consisting of crushed particles of sintered material comprising 100parts by weight of calcium oxide, and 3 to 50 parts by weight of atleast two compounds, at least one of said two compounds being up to 40parts by weight, in terms of sodium carbonate, of at least one compoundselected from the group consisting selected from the group consisting ofup to 30 parts by weight of calcium fluoride, sodium fluoride, magnesiumfluoride, barium fluoride, and sodium silicofluoride.

5. A granular desulfurizer composition for quickly desulfurizing pigiron in off-furnace treatment according to claim 1, characterized inthat said sintered "material comprises a binding amount of a binderselected from the group consisting of sodium dihydrogen clay.

6. A method of making granular desulfurizer composition for quicklydesulfurizing pig iron in off-furnace treatment, comprising steps ofthoroughly mixing parts by weight of particles of calcium oxide, saidcalcium oxide particles being not greater than 0.3 mm in diameter, and 3to 50 parts by weight, in total, of particles of at least one compoundselected from the group consisting of up to 30 parts by weight ofcalcium fluoride, sodium fluoride, magnesium fluoride, barium fluorideand sodium silicofluoride, and up to 40 parts by weight, in terms ofsodium carbonate, of at least one compound selected from the groupconsisting of sodium carbonate, sodium hydroxide and sodium oxide,

said compound particles being not greater than 0.3 mm in diameter;sintering the mixture thus prepared at 800C to 1,600C, whereby thesulfur content is substantially reduced and so as to bind said calciumoxide particles with said compound; and crushing the material thussintered into a particle size of 4 mm or smaller; whereby the pig ironis substantially desulfurized in an off-furnace treatment.

I :l: =r

phosphate, calcium chloride, starch, and

1. A granular desulfurizer composition for quickly desulfurizing pig iron in off-furnace treatment consisting of crushed particles of material sintered at a temperature of 800*-1,600* C, whereby the sulfur content is substantially reduced, comprising 100 parts by weight of calcium oxide and 3 to 50 parts by weight, in total, of at least one compound selected from the group consisting of up to 30 parts by weight of calcium fluoride, sodium fluoride, magnesium fluoride, barium fluoride, and sodium silicofluoride, and up to 40 parts by weight, in terms of sodium carbonate, of at least one compound selected From the group consisting of sodium carbonate, sodium hydroxide, and sodium oxide, the particle size of said desulfurizer composition being smaller than 4 mm and each granule of said desulfurizer composition includes calcium oxide particles of not greater than 0.3 mm diameter which are bonded by said compound, whereby the pig iron is substantially desulfurized in an off-furnace treatment.
 2. The granular desulfurizer composition according to claim 1, consisting of crushed particles of sintered material comprising 100 parts by weight of calcium oxide and 3 to 30 parts by weight of at least one compound selected from the group consisting of calcium fluoride, sodium fluoride, magnesium fluoride, barium fluoride and sodium silicofluoride.
 3. The granular desulfurizer composition according to Claim 1, consisting of crushed particles of sintered material comprising 100 parts by weight of calcium oxide and 3 to 40 parts by weight, in terms of sodium carbonate, of at least one compound selected from the group consisting of sodium carbonate, sodium hydroxide, and sodium oxide.
 4. The granular desulfurizer composition according to Claim 1, consisting of crushed particles of sintered material comprising 100 parts by weight of calcium oxide, and 3 to 50 parts by weight of at least two compounds, at least one of said two compounds being up to 40 parts by weight, in terms of sodium carbonate, of at least one compound selected from the group consisting of sodium carbonate, sodium hydroxide and sodium oxide, while the other one of said two compounds being selected from the group consisting of up to 30 parts by weight of calcium fluoride, sodium fluoride, magnesium fluoride, barium fluoride, and sodium silicofluoride.
 5. A granular desulfurizer composition for quickly desulfurizing pig iron in off-furnace treatment according to claim 1, characterized in that said sintered material comprises a binding amount of a binder selected from the group consisting of sodium dihydrogen phosphate, calcium chloride, starch, and clay. 